WASHINGTON — The U.S. trade deficit narrowed sharply in December because oil imports plummeted and total exports rose. The smaller trade gap means the economy likely performed better in the final three months of last year than first estimated last week. The Commerce Department says the trade deficit fell nearly 21 percent in December. That left the trade deficit at $38.6 billion, the smallest in nearly three years. Exports rose 2.1 percent to $186.4 billion. Exports of oil and other petroleum products rose to the highest level on record. Imports shrank 2.7 percent to $224.9 billion. Oil imports plunged to 223 billion barrels, the lowest since February 1997. A narrower trade gap boosts growth because it means U.S. companies earned more from overseas sales while consumers and businesses spent less on foreign products.